Sky-Watcher Classic 250P Dobsonian
The Sky-Watcher Classic 250P Dobsonian 254mm/1200mm (10″) has a “paraboloidal” primary mirror to eliminate spherical aberration. It also has a four-arm, secondary- mirror bracket with fine supports (0.5mm thick), to reduce diffraction spikes and light loss. In addition, this model includes a 2″ focuser with a 1.25″ adapter, allowing the use of either eyepiece size. This model also include the new feature-tension control handle.
What is Dobsonian Telescope and why the Tension Control Handle?
A simple, elegant form of an alt-azimuth mount made to carry a Newtonian reflector. It was popularized by John Dobson in the late 1970’s. The Dobsonian mounted telescope is popular among amateur astronomers and telescope makers because of its simplicity. The Dobsonian mount consists of a box which allows the optical tube assembly for pivoting in altitude. The box itself is swiveled on a base in azimuth.
The Dobsonian mount usually relies on the friction between the side bearings on the optical tube of the telescope and a frictional material on the saddle to hold the optical tube in place. If there is too much friction, the telescope is difficult to move. Making centring an object in the field of view hard. If there is too little friction, the telescope will not stay where it is positioned. This makes stabilizing the optical tube of the telescope difficult, especially when accessories, such as a finderscope or an eyepiece, are added to the optical tube. As long as the amount of friction is at an appropriate level. The telescope can remain in its desired position to view an object and maintain its position even when the mount is rotated.
The devices for stabilizing a telescope on the Dobsonian mount currently available include a sliceable weight to counterbalance the weight of the telescope, a friction lock that must be adjusted to inhibit movement of the telescope, and a spring attached to the telescope tube and mount to aid in stabilization. These devices are inconvenient to use because they do not provide a simple and user-friendly way to adjust the friction.
The object of the Sky-Watcher Tension Control Handle invention (Patented) is to provide a tension adjuster that users can easily turn to add or reduce tension, thereby increasing or decreasing the friction between the optical tube and the sideboard of the mount. By providing such a tension adjuster, the telescope does not need to be balanced in order to stay in position. The tension adjuster can be tightened such that the optical tube can stay in a position but can still be moved when prompted to adjust the position of the optical tube. Alternatively, the tension adjuster can be completely tightened to lock the optical tube in position.